PaleoBios 33:1–28, February 8, 2016 PaleoBios

OFFICIAL PUBLICATION OF THE UNIVERSITY OF CALIFORNIA MUSEUM OF PALEONTOLOGY

Suzanne G. Strait, Patricia A. Holroyd, Carrie A. Denvir and Brian D. Rankin (2016). Early Eocene (Wasatchian) rodent assemblages from the Washakie Basin, Wyoming.

Cover photo: Howard Hutchison excavating at V71237 (Lower Meniscotherium) during July 1971. Polaroid image from field notes of Barbara T. Waters, on file at UCMP. Citation: Strait, S. G., Holroyd, P. A., Denvir, C. A. & Rankin, B. D. 2016. Early Eocene (Wasatchian) rodent assemblages from the Washakie Basin, Wyoming. PaleoBios, 33(1). ucmp_paleobios_29986. PaleoBios 33:1–28, February 8, 2016

Early Eocene (Wasatchian) rodent assemblages from the Washakie Basin, Wyoming

SUZANNE G. STRAIT1, PATRICIA A. HOLROYD2*, CARRIE A. DENVIR1 and BRIAN D. RANKIN2

1Department of Biological Sciences, Marshall University, Huntington, West Virginia 25755 U.S.A. 2University of California Museum of Paleontology, Berkeley, California 94720 U.S.A.

Rodent assemblages are described from two early Eocene (Wasatchian North American Land Mammal Age; Graybul- lian subage) localities from the Main Body of the Wasatch Formation in the Washakie Basin, Wyoming. One locality (UCMP V71237) represents a catastrophic death assemblage and the other (UCMP V71238) is a channel lag which immediately overlies it. Quarrying and screen-washing at these localities has resulted in the recovery of 81 speci- mens from V71237 and 224 specimens from V71238 and comprising a uniquely rich, stratigraphically controlled sample. The rodent fauna from these localities include Paramys copei, P. taur u s , Lophiparamys murinus, Micropara- mys hunterae, Tuscahomys ctenodactylops, and Knightomys cf. K. minor. These specimens provide substantial new morphological data for the previously poorly-known M. hunterae, T. ctenodactylops, and L. murinus. Comparison of relative abundances demonstrates that T. ctenodactylops is the most common in both localities, but that the smaller bodied species M. hunterae and Knightomys cf. K. minor are much rarer in the lag deposit.

Keywords: Wasatch Formation, Mammalia, Rodentia, diversity, abundance

INTRODUCTION UCMP V71238 is a massive, moderately-indurated sand- Rodents are still relatively poorly known from North stone unit that immediately overlies the mudstone of V71237 American early Eocene assemblages, and localities that (Fig. 2). In V71238 fossils are found as lag in approximately produce abundant, relatively complete specimens are rare. 10 cm at the base of this sandstone unit and appear to rep- Here we describe two rodent assemblages that have produced resent a direct reworking of the underlying mudstone unit. both. These assemblages derive from two localities, UCMP Fossils are recovered from this unit primarily as eroded V71237 (Lower Meniscotherium) and UCMP V71238 (Upper float, and weathered parts of this unit were screen-washed Meniscotherium) that occur approximately 40 meters above to recover small specimens. the base of the Wasatch Formation in the Washakie Basin Williamson and Lucas (1992) and Williamson (2001) pre- (Fig. 1), an area that in the Eocene had low topographic relief sented brief faunal lists for UCMP V71237; Table 1 provides with permanently saturated soils, localized ponds, and large an updated faunal list and Table 2 a comparison between lo- channels (Roehler 1993). UCMP V71237 is an approximately calities V71237 and V71238 based on data generated by more one meter thick muddy siltstone unit that contains a cata- recent work with the UCMP collection. These new data have strophic assemblage that appears to have formed within days greater biostratigraphic utility. Rankin and Holroyd (2014) after the death of the animals (Williamson 2001). This local- inferred both UCMP V71237 and V71238 to be early Wasat- ity is dominated by remains of the eponymous condylarth chian (Wa3 of Gingerich 1983; Graybullian subage) based Meniscotherium tapiacitum Cope, 1882b. Fossils were hand- on the co-occurrence of Homogalax protapirinus (Wortman, quarried, and the remaining matrix was screen-washed to 1896), Cardiolophus semihians (Cope, 1882a), Tetonius mat- recover additional specimens (J.H. Hutchison, pers. comm. thewi Bown and Rose, 1987, Cantius mckennai Gingerich and field notes on file at UCMP). Some of the rodent speci- and Simons, 1977, and Haplomylus speirianus (Cope, 1880b) mens described here were found during the initial quarrying (see biostratigraphic ranges for these taxa in Gingerich 1983, operation, but the majority were recovered by subsequent 1991, Bown and Rose 1987, Clyde 1997, Chew 2005). Based screen-washing. on the range of this biozone in the Bighorn Basin, the age of V71237 and V71238 can be estimated to be approximately *author for correspondence 54 Ma (Wing et al. 2000). Citation: Strait, S. G., Holroyd, P. A., Denvir, C. A. & Rankin, B. D. 2016. Early Eocene (Wasatchian) rodent assemblages from the Washakie Basin, Wyoming. PaleoBios, 33(1). ucmp_paleobios_29986. Permalink: http://escholarship.org/uc/item/6946n7r3 Copyright: Items in eScholarship are protected by copyright, with all rights reserved, unless otherwise indicated. 2 PALEOBIOS, VOL. 33, FEBRUARY 2016

SYSTEMATIC PALEONTOLOGY

Abbreviations and nomenclature FMNH – Field Museum of Natural History, Chicago, Il- linois, USA; UCMP – University of California Museum of Paleontology, Berkeley, California, USA; UM – University of Michigan, Ann Arbor, Michigan, USA; UW – University of Wyoming, Laramie, Wyoming, USA. Upper teeth are designated by upper case letters; teeth of the lower denti- tion by lower case letters. Specimens bearing more than one tooth are indicated by dashed tooth positions (e.g., M1-2); specimens whose position is indeterminate are indicated by Figure 1. Map showing locations of the Lower (UCMP V71237) slashed tooth positions (e.g., M1/2). All measurements are and Upper (UCMP V71238) Meniscotherium localities and the in mm and were taken on a Nikon SMZ800 or Leica M125 other rodent faunas discussed in the text. with ocular micrometers. All measurements were repeated for precision by different researchers. Length = L; width = W; trigonid width = TrW; talonid width = TaW; observed range = OR; standard deviation = SD. Dental nomenclature is as shown in Figure 3 and follows Wood (1962) and Korth (1994).

RODENTIA Bowdich, 1821 SCIUROMORPHA Brandt, 1855 ISCHYROMYIDAE Alston, 1876 PARAMYINAE (Haeckel, 1895) Paramys Leidy, 1871 Paramys copei Loomis, 1907 Fig. 4

Referred specimen—UCMP V71238: UCMP 148758, LM1/2. Description and Discussion—UCMP 148758 is a rela- tively large (L= 3.1, W=3.4) isolated M1/2 that conforms morphologically to those described for Paramys copei by Wood (1962), Korth (1984), and Ivy (1990), and is referred Figure 2. Outcrop of V71237 and V71238, taken in July 2015. here to that taxon. Second author (approximately 160 cm for scale). Paramys taurus Wood, 1962 Together, the fauna from these two localities can serve as Figs. 4, 5; Tables 3, 4 a window into the composition of an early Eocene rodent Referred specimens—UCMP V71237: UCMP 148614, fauna from a floodplain environment. Many previously- 148629, Rp4; UCMP 148630, Lp4; UCMP 148672, Rm1/2; described Wasatchian rodents are from surface collections UCMP 148631, Rm3; UCMP 149222, Right dentary with that may have accumulated over considerable spans of time m3; UCMP 148634, LM3. and also tend to be size biased. Additionally, few single lo- UCMP V71238: UCMP 148748, Lp4; UCMP 148749, calities have sample sizes that approach UCMP V71237 and 151272, Rm1/2; UCMP 148747, Lm1/2; UCMP 148755, V71238. Comparison of the two localities provides insights 189311, Rm3; UCMP 148751, 148752, 148756, 151273, into how differences in depositional environment can pro- 151274, Lm3; UCMP 148757, LP4; UCMP 148731, 189305, duce significantly different perceptions of dominance and RM1/2; UCMP 148720, 148759, 151357, LM1/2; UCMP relative abundances of small mammals. 148784, 189301, LM3. STRAIT ET AL.—EARLY EOCENE RODENTS FROM WYOMING 3 Marsh, 1876b Marsh, Korth, 1984 ) ( Korth, pernix ) Wortman, 1896 ) ( Wortman, Matthew, 1918 ) ( Matthew, ( Cope, 1882a ) ( Cope, 1880b ) Cope, 1882a Sinclair, 1914 Sinclair, Gazin, 1962 Leidy, 1870 Leidy, Miller and Gidley, 1918 Gidley, Miller and Wood, 1962 Wood, Marsh, 1894 Marsh, Cope, 1874 Cope, 1881 Trouessart, 1879 Trouessart, Matthew, 1915 sp. Matthew, sp. 2009 Dawson, Beard and Simpson, 1940 Simpson, Osborn and Wortman, 1892 Wortman, and Osborn Alston, 1876 Alston, Peterson, 1919 Peterson, Turner, 1879 Turner, Ivy, 1990 Ivy, K. minor cf. (= Hyracotherium Leidy, 1872 sp. Leidy, Gingerich and Simons, 1977 sp. Simons, and Gingerich Matthew, 1918 Matthew, sp. Cope, 1875b Trouessart, 1879 Trouessart, Owen, 1848 Trouessart, 1879 Trouessart, Cope, 1881 Gray, 1821 Gray, Owen, 1848 Choctawius Bowdich, 1821 Bowdich, Linnaeus, 1758 Genus and species indeterminate and Genus cf. Phenacolemur matthewi Rose, 1987 Bown and Tetonius pearcei Tetonoides 1977 Simons, and Gingerich mckennai Cantius Copelemur paulus Hyopsodus Microsyops Apheliscus Haplomylus speirianus Haplomylus Cope, 1882b tapiacitum Meniscotherium Ectocion osbornianus Arenahippus Cardiolophus semihians Homogalax protapirinus Bunophorus robustus Lophioparamys murinus 1990 Ivy, hunterae Microparamys Paramys taurus Loomis, 1907 copei Paramys ctenodactylops Tuscahomys Knightomys Paromomyidae Paromomyidae Omomyidae Hyopsodontidae Microsyopidae Microsyopidae Adapidae Apheliscidae Meniscotheriidae Meniscotheriidae Phenacodontidae Equidae Isectolophidae Dichobunidae Homacodontinae Ischyromyidae Cylindrodontidae Sciuravidae Condylarthra Primates

Perissodactyla Rodentia

Artiodactyla McKenna, 1960 McKenna, Gazin, 1962 Wortman, 1902 Wortman, Wortman, 1903 Wortman, Marsh, 1876a Marsh, sp. Rose, 1979 Bown and Matthew, 1910 Matthew, Leidy, 1869 Leidy, Matthew, 1901 sp. Matthew, McKenna, 1975 McKenna, Schlosser, 1887 Schlosser, Matthew, 1929 sp. Matthew, Winge, 1917 Winge, Cope, 1883 sp. Owen, 1845 Simpson, 1928 Simpson, sp. 1987 Gingerich, Cope, 1884b Matthew, 1899 sp. Matthew, Matthew, 1909 Matthew, Matthew and Granger, 1921 sp. Granger, and Matthew Scott and Jepsen, 1936 Jepsen, and Scott sp. Cope, 1874 Gill, 1872 Gill, Gregory, 1910 Gregory, Matthew, 1918 Matthew, Gregory, 1910 Gregory, Cope, 1880a Cope, 1873 Cope, 1875a Weber, 1904 Weber, Marsh, 1875 Marsh, McKenna, 1975 McKenna, Bowdich, 1821 Bowdich, McKenna, 1975 McKenna, 1975 McKenna, Palaeictops Prodiacodon species indeterminate and Genus Limnocyoninae Peradectes protinnominatus Mimoperadectes species indeterminate and Genus Leptacodon Wyonycteris species indeterminate and Genus 2014 Rankin Holroyd, and dulcis Aceroryctes sp. 1872 Marsh, Apatemys Coryphodon Amaramnis gregoryi Palaeosinopa species indeterminate and Genus Esthonyx Hyaenodontidae Hyaenodontidae Adapisoricidae Adapisoricidae Nyctitheriidae Leptictidae Apternodontidae Didelphodonta Palaeoryctidae Apatotheria Apatemyidae Coryphodontidae Pantolestidae Metacheiromyidae Esthonychidae Miacidae Order Uncertain Order Creodonta Erinacemorpha Soricomorpha Leptictida Cimolesta Pantodonta Pantolesta ?Pholidota Palaeanodonta Tillodonta Carnivora Norell et al., 1994 al., et Norell Hutchison, 2013 Hutchison, sp. 1921 Mook, Archibald and Hutchison, 1979 Hutchison, and Archibald

Ameghino, 1890 Ameghino, Hutchison, 2013 Hutchison, sp. Lacépède, 1803 sp. 1930 Jepsen, Hay, 1892 Hay, Cuvier, 1825 Cuvier, Crochet, 1979 Crochet, Estes et al., 1988 et al., Estes 1900 sensu Fürbringer, Matthew and Granger, 1921 sp. Granger, and Matthew sensu sensu 1807 Cuvier, Hay, 1929 Hay, Cope, 1884a Gill, 1872 Gill, Cope, 1882a Wagler, 1831 Wagler, Bonaparte, 1838 Bonaparte, Cuvier, 1817 Cuvier, Hay, 1929 Hay, Batsch, 1788 Batsch, Benton and Clark, 1988 Clark, and Benton sensu 1789 Gmelin, Allognathosuchus Lepisosteus Oppel, 1811 Oppel, Parectypodus Ectypodus ( Cope, 1872 ) testudinea Echmatemys species indeterminate and Genus Genus and species indeterminate and Genus Planetochelys dithyros Planetochelys Genus and species indeterminate and Genus species indeterminate and Genus gaffneyi Palatobaena cf. cf. Genus and species indeterminate and Genus cf. Neoplagiaulacidae Neoplagiaulacidae Peradectidae Kinosternidae Kinosternidae Planetochelyidae indeterminate Family indeterminate Family Iguania Iguania Baenidae Anguimorpha Anguimorpha Amiidae Lepisosteidae Alligatoridae . Taxonomic listing of vertebrates from UCMP V71237 and V71238, Wasatch Formation, Wyoming. Formation, V71238, Wasatch UCMP V71237 and from vertebrates of listing . Taxonomic

Didelimorphia

Linnaeus, 1758 Aves Anseriformes 1758 Linneaus, Mammalia Multituberculata

Testudines

Squamata Huxley, 1880 Huxley, Osteichthyes Amiiformes Lepisosteiformes Linnaeus, 1758 Reptilia Crocodylia Table 1 4 PALEOBIOS, VOL. 33, FEBRUARY 2016

Figure 4. Paramys spp. upper dentition. A. Paramys taurus, UCMP V71238/148757, left P4, B. Paramys copei, UCMP V71238/148758, left M1/2, C. Paramys taurus, V71237/148634, left M3. Scale bar = 1 mm.

Figure 3. Schematic upper (A) and lower molar (B) showing dental nomenclature, modified after Wood (1962) and Korth (1994). Upper molar: 1. anteroloph, 2. paracone, 3. protocone, 4. protoloph, 5. metaconule, 6. protoconule (paraconule of stan- dardized tribosphenic dental nomenclature), 7. mesostyle, 8. metacone, 9. metaloph, 10. hypocone, 11. posteroloph. Lower molar: 1. anterior cingulid, 2. protoconid, 3. metaconid, 4. Figure 5. Examples of the lower dentition of Paramys taurus. A. mesostylid, 5. anterolophid, 6. metalophulid II (metalophid of UCMP V71237/148672, right m1/2, B. UCMP V71238/151272, Wood 1962), 7. mesoconid, 8. ectolophid, 9. hypoconid, 10. en- right m1/2. C. UCMP V71238/151273, left m3, D. UCMP toconid, 11. hypolophid, 12. hypoconulid, 13. posterolophid. V71238/151274, left m3. Scale bar = 1 mm. STRAIT ET AL.—EARLY EOCENE RODENTS FROM WYOMING 5 V71238 X X X X X X X X X X X X X X X X X X X V71237 X X X X X X X X X X X X X X X X X X X X X X - - sp . sp . sp. Metacheiromyidae genus and species inde terminate Esthonyx Miacidae genus and species indeterminate Tetonius matthewi Tetonius pearcei Tetonoides minate Limnocyoninae genus and species indeter Microsyops sp. Microsyops cf . Choctawius sp Phenacolemur Cantius mckennai Copelemur sp . Hyopsodus paulus Apheliscus Haplomylus speirianus Meniscotherium tapiacitum Ectocion osbornianus (=Hyracotherium) pernix Arenahippus Cardiolophus semihians Cardiolophus Homogalax protapirinus Bunophorus robustus Lophioparamys murinus Microparamys hunterae Microparamys Paramys taurus Paramys copei ctenodactylops Tuscahomys Knightomys cf . K. minor X X V71238 X X X X X X X X X X X X X X X X X X X X X V71237 X X X X X X X X X X X X X X X X X - - -

sp.

sp. sp. sp. sp. sp. protinnominatus sp. Kinosternidae genus and species indeterminate Adapisoricidae genus and species indeterminate Planetochelys Echmatemys testudinea Amiidae genus and species indeterminate cf. Lepisosteus sp. Leptacodon sp. nate Anseriformes genus and species indetermi Ectypodus Parectypodus cf. Allognathosuchus Wyonycteris Palaeictops Peradectes Anguimorpha genus and species indetermi nate sp. Prodiacodon Mimoperadectes sp. Iguania genus and species indeterminate Palatobaena gaffneyi Apternodontidae genus and species indeter minate dulcis Aceroryctes Apatemys sp. Coryphodon sp. Amaramnis gregoryi Palaeosinopa Taxonomic comparisons of vertebrates from UCMP V71237 and V71238, Wasatch Formation, Wyoming. Formation, V71238, Wasatch UCMP V71237 and from vertebrates of comparisons 2. Taxonomic Table 6 PALEOBIOS, VOL. 33, FEBRUARY 2016

Table 3. Measurements and descriptive statistics of the upper dentition of Paramys taurus from UCMP V71237 and V71238, Wasatch Formation, Wyoming.

M1/M2 M3 L W L W 148720 2.2 2.6 148731 2.2 2.5 148759 2.3 2.6 151357 2.6 3.3 189305 2.2 2.6 148634 2.4 2.7 148784 2.4 2.4 189301 2.4 2.7

OR 2.2-2.6 2.5-3.3 2.4 2.4-2.7 Mean 2.3 2.72 2.40 2.60 SD 0.17 0.33 0 0.17 Table 4. Measurements and descriptive statistics of the lower dentition of Paramys taurus from UCMP V71237 and V71238, Wasatch Formation, Wyoming.

p4 m1/m2 m3 L TrW TaW L TrW TaW L TrW TaW 148614 2.3 1.6 1.8 148629 2.3 1.6 1.9 148630 2.3 1.5 1.8 148748 2.2 1.5 1.9 148672 2.7 2.3 2.5 148747 - 1.9 2.4 148749 2.7 2.2 2.2 151272 2.8 2.2 2.5 148631 3.2 2.2 2.1 148751 3.3 2.2 2.2 148752 3.3 2.3 2.1 148755 3.1 2.0 2.0 148756 3.1 2.0 2.0 151273 2.8 2.1 1.9 151274 3.3 2.1 2.0

OR 2.2-2.3 1.5-1.6 1.8-1.9 2.7-2.8 1.9-2.3 2.2-2.5 2.8-3.3 2.0-2.3 1.9-2.2 Mean 2.28 1.55 1.85 2.73 2.15 2.40 3.16 2.13 2.04 SD 0.05 0.06 0.06 0.06 0.17 0.14 0.18 0.11 0.10 STRAIT ET AL.—EARLY EOCENE RODENTS FROM WYOMING 7

Description and Discussion—These specimens are crenulate but less columnar and topographically lower, dis- referred to Paramys taurus based on lower teeth with a tinct hypoconulid present on lower molars, anteroposteriorly dominant, obliquely oriented metaconid, trigonid basin re- more transverse upper dentition with shorter protocone arm stricted to a narrow fissure, strong posterolphids with lophate (sensu Flanagan 1986), P4 metacone is only slightly smaller hypoconulids, talonid cusps marginally placed, and promi- than the paracone, and P4 lacks a paracone arm (sensu Fla- nent mesoconids. Teeth are variable with wear. In unworn nagan 1986). Wood (1962) included as diagnostic characters specimens enamel pitting is evident, as are mesostylids. Worn of L. murinus a “strong metalophulid on molars” and acces- specimens show ectolophid development and posterolophid sory cuspules on m3. This character should be emended to continuity with the entoconid. The trigonid basin size varies a strong metalophulid II on m1-2 and variable development with wear, from a more open condition in unworn specimens of accessory cuspules of m3. Smaller than L. woodi Guthrie, but a narrow fissure develops with greater wear. A small ac- 1971 with coarser crenulations. cessory cuspule is present on one specimen (UCMP 148752) Description—The following descriptions of lower denti- anterior to the posterolophid. The single P4 (UCMP 148757) tion morphology are additions to those of Matthew (1918), from these localities is completely unworn and has equally Wood (1962), and Ivy (1990). small hypocone and protoconule. Due to the lack of wear p4—The metalophulid II is continuous transversely from there is no metaloph or protoloph development. There is the protoconid and ascends up the center of the posterior wall a small accessory cuspule buccal to the metacone. A small, of the metaconid. There is a short, curved anterolophid that salient mesostyle is present anterobuccal of the metacone. arises from the midpoint of the protoconid and terminates at the labial base of the metaconid. A mesoconid is evident, MICROPARAMYINAE Wood, 1962 although it is incorporated into the talonid crenulations. Lophiparamys Wood, 1962 A mesostylid is present. The entoconid and hypoconid Lophiparamys murinus (Matthew, 1918) are distinct. A posterolophid connects the hypoconid to a Fig. 6; Tables 5, 6 cuspule just labial of the entoconid, which may represent a Referred specimens—UCMP V71237: UCMP 148785, hypoconulid. Rp4; UCMP 148786, RP4; UCMP 149221, LP4; UCMP m3—The trigonid crests and basin of the m3 are reduced. 148674, LM1/2. The anterolophid is discontinuous with the protoconid, and UCMP V71238: UCMP 148688, 148690, 148691, Lm3; the metalophulid II is only visible in worn teeth. A distinct UCMP 151276, LP4; UCMP 235522, LM1/2; UCMP 151277, mesostylid is present and is similar in size to the mesoconid, RM3. however, with wear the mesostylid become less distinctive. In Emended Diagnosis—Lophiparamys murinus differs describing the type, Wood (1962) noted the presence of four from L. debequensis Wood, 1962 in its larger size, enamel cuspules between the hypoconid and mesostylid. In the sam- ple at hand, both the hypoconulid and entoconid are present Table 5. Measurements and descriptive statistics of the lower but no additional cuspules are developed, demonstrating the dentition of Lophiparamys murinus from UCMP V71237 and V71238, Wasatch Formation, Wyoming. Table 6. Measurements and descriptive statistics of the lower P4 M1/M2 M3 dentition of Lophiparamys murinus from UCMP V71237 and V71238, Wasatch Formation, Wyoming. L W L W L W 148786 1.6 2.2 p4 m3 149221 1.6 2.2 L TrW TaW L TrW TaW 151276 1.5 2.0 148785 1.6 1.2 1.4 148674 1.8 2.2 148688 2.1 1.6 1.5 235522 2.0 2.3 148690 2.6 1.8 1.7 151277 2.0 1.8 148691 2.2 1.6 1.5

OR 1.5-1.6 2.0-2.2 1.8-2.0 2.2-2.3 - - OR - - - 2.1-2.6 1.6-1.8 1.5-1.7 Mean 1.57 2.13 1.90 2.25 - - Mean - - - 2.30 1.67 1.57 SD 0.06 0.12 0.14 0.07 - - SD - - - 0.26 0.12 0.12 8 PALEOBIOS, VOL. 33, FEBRUARY 2016

Figure 6. Lophiparamys murinus. A. UCMP V71237/148786, right P4, B. UCMP V71237/148674, left M1/M2, C. UCMP V71238/151277, left M3, D. V71237/148785, right p4, E. UCMP V71238/148688, right m3. Scale bar = 1 mm. variability in the crenulate occlusal morphology. M1 or M2 of L. murinus. Both teeth are similar in general The upper dentition has not been previously described morphology to P4 except that the anteroloph on these molars for Lophioparamys murinus. Six upper teeth are attributed is better developed and more anteriorly projecting. to L. murinus based on size and distinctive crenulate enamel. M3—The crown of UCMP 151277 is dominated by a large, P4—Unlike the reduced metacone on the P4 of L. debe- rounded protocone and slightly smaller paracone; these cusps quensis, the P4 of L. murinus displays a metacone that is only are joined by a distinct protoloph. The metacone is indistinct slightly smaller than the paracone. The hypocone is distinct, and the area it would normally occupy is merely a flattened, but smaller than the protocone. A posteroloph extends from crenulated area confluent with the crenulated trigon basin. the hypocone to the posterolabial corner of the metacone. No hypocone is present. A small protoconule is developed, There is a small, anteroposteriorly compressed mesostyle. however, the presence or absence of a metaconule cannot be The metaconule is doubled, whereas the protoconule is only determined due to the extent of crenulation. A short, weak a single cusp. Due to the crenulated nature of these teeth, metaloph originates from the protocone but only extends both the posteroloph and metaloph are discontinuous. With approximately to the midpoint of the tooth. The anteroloph wear, the lophs become more prominent and converge on arises from near the base of the protocone and extends to the the protocone. The anteroloph originates at the midpoint of labial edge of the tooth; the enamel of the anteroposteriorly the protocone. A short protocone crest (sensu Korth 1994) short shelf formed by this loph is crenulate. In comparison extends between the anteroloph and the protoconule. The to Lophiparamys debequensis, the shape of the tooth in L. paracone arm, observed within the P4 of L. debequensis (see murinus is less triangular and more subrectangular in oc- Flanagan 1986), is not developed. clusal outline. M1/2—UCMP 148674 and 235522 represent either the Discussion—Specimens of Lophiparamys are STRAIT ET AL.—EARLY EOCENE RODENTS FROM WYOMING 9 comparatively rare in Eocene fossil assemblages. Lophipa- UCMP 148770, 148775, 148776, 148778-148780, Lm1/2; ramys murinus was first described by Matthew (1918) based UCMP 148777), Rm3; UCMP 148771, Lm3; UCMP 148762, on an upper and lower dentition. Subsequently, the upper 148763, 148766, 148768, RM1/2; UCMP 148769, LM1/2. dentition was lost and had never been figured. Ivy (1990) Emended diagnosis—Ivy’s (1990) original diagnosis of included two additional dentaries with a single molar each. Microparamys hunterae included: same size as Knightomys Our sample includes the first occurrence of L. murinus from (formerly Microparamys) reginensis (Korth, 1984) but with outside the Bighorn Basin and allows us to provide the first only one mental foramen; smaller with a less elongated me- detailed description of upper teeth, thereby permitting more soconid than M. scopaiodon Korth, 1984, smaller than M. diagnostic characters to be identified. The upper teeth de- minutus (Wilson, 1937) and M. cheradius Ivy, 1990; further scribed here are relatively primitive among microparamyines differs from M. cheradius with a less complete, more oblique due to their subrectangular shape with greater width relative metalophulid II, and less well separated anterolophid. With to length when compared to the squarer outline seen in most the reallocation of “M.” reginensis to Knightomys (Flanagan microparamyines. In its molar proportions, retention of a 1986), M. hunterae is now the smallest known species of distinct hypoconulid on the lower molars, distinct conules Microparamys. on upper molars, and less extreme crenulation, L. murinus Upper dentition and p4 diagnostic characters can now be appears to be the least derived species of the genus. added to Ivy’s original description including: differs from Lophiparamys woodi is the most poorly known species of M. cheradius in lacking a P4 mesostyle and having better Lophiparamys, with only six isolated teeth reported (Guthrie developed cingula and relatively larger hypocone, giving 1971). The original diagnosis for this species is problematic. the tooth a much squarer outline; M1/2 paracone larger Guthrie (1971, p. 73) noted as a diagnostic character “lower and higher than metacone; M1/2 mesostyle present; M1/2 molars with ... protoconid not connected to anterior cingu- protoloph and metaloph typically discontinuous. Differs lum,” even though the only lower tooth position known for from M. scopaiodon in that the p4 is double rooted, relatively L. woodi is m3. A distinctive valley, especially evident in un- larger (p4s are approximately the same absolute size in both worn specimens, separating the protoconid and anteroloph taxa, but the molars in M. scopaiodon much larger), and is primitive for Microparamyini and is most distinctive in hypoconid slightly larger. posterior molars (Wood 1962, Korth 1984, Ivy 1990). The Description—Microparamys hunterae was previously second diagnostic character of L. woodi Guthrie noted was only known from the moderately worn type specimen (Fig. lower molars with the entoconid isolated from posterior 7H) from the early Wasatchian (Wa-2) of the Clarks Fork cingulum. Entoconid isolation in unworn specimens is di- Basin. This new sample includes the first evidence of the agnostic of Microparamyini as well (Wood 1962). Based on upper dentition, p4, and deciduous teeth, and also permits Guthrie’s available sample of L. woodi, there are few tooth the examination of variation in the lower dentition. positions that can be compared across taxa; therefore the p4—The metaconid is the largest and highest cusp and is distinctiveness between L. murinus and L. woodi is limited located anterior and lingual to the shorter protoconid. These to size and degree of crenulation. two cusps are separated by a deep fissure in the unworn speci- men. A short metalophulid II arises from the protoconid, Microparamys Wood, 1959 running lingually and ending at the base of the metaconid. Microparamys hunterae Ivy, 1990 A tiny anteroconid, present immediately anterior to the (Fig. 7; Tables 7-10) protoconid, disappears with wear. The trigonid basin is open labially, and no ectolophid is present. In unworn specimens Referred specimens—UCMP V71237: UCMP 148610, a small, rounded mesoconid is evident. Posteriorly, the tal- right dentary with p4, m1-3; UCMP 148648, 148656, Lp4; onid basin is closed by a low crest joining hypoconid and UCMP 148671, Lm1; UCMP 148654, 148658, 148659, entoconid. No distinct hypoconulid is discernable. 149219, 149224, Rm1/2; UCMP 148643, 148660, 148663, m1/2—Anteroposteriorly compressed trigonid with Lm1/2; UCMP 148655, Rm3; UCMP 148675, LDP4; UCMP 148650, LP4, UCMP 148638, 152488, RM1-2; UCMP metaconid that is higher and more obliquely oriented than 148611, LM1-2; UCMP 148647, 148651-148653, 148665, the protoconid. Anterolophid well developed enclosing the 148667, 148670, RM1/2; UCMP 148640, 148641, 148645, trigonid anteriorly, but it is not continuous with the protoco- 148666, 148669, LM1/2; UCMP 148639, left maxilla with nid until later wear stages. Metalophulid II does not ascend M2+alveolus of M3; UCMP 148642, 148668, RM3; UCMP the metaconid, instead ending near the posteromedial edge 148761, 148676, LM3. of that cusp. Mesoconids are round, isolated, and do not UCMP V71238: UCMP 148772, 148774, 148782, Rm1/2; elongate into the talonid basin. Metastylids lacking. The 10 PALEOBIOS, VOL. 33, FEBRUARY 2016

Figure 7. Microparamys hunterae from UCMP V71237. A. UCMP 148675, left DP4, B. UCMP 148650, left P4, C. UCMP 148611, left maxillary fragment with M1-M2, D. UCMP 148668, right M3, E. UCMP 148648, left p4, F. UCMP 148660, left m1/2, G. UCMP 148610, right dentary with p4-m3, H. UM 66968, holotype, right dentary with partial m1, m2, partial m3. Scale bar for A-G = 1 mm and is located between A and F. Scale bar for G-H = 1 mm. posterolophid is continuous with an anterior-posteriorly the metacone, and the mesostyle is very small. There is a compressed, centrally-positioned, small hypoconulid. The small hypocone, and the hypocone and protocone are closer entoconid is isolated. together than in the molars. m3—m3 differs from m1/2 in that the hypoconid is more P4—The upper premolar is relatively shorter than the compressed and continuous with the more lingually posi- molars, but still basically square in shape. The paracone tioned hypoconulid. and metacone are not marginal; there is a discontinuous Dentary—Part of the dentary is preserved in UCMP cingulum that extends across the buccal margin of the tooth. 148610. The full depth of the dentary is not preserved, so we An anteroloph begins low at the base of the protocone and cannot assess whether it is as deep as the specimen described extends around to the labial margin of the tooth where it by Ivy (1990). Also, although the bone immediately beneath widens at the paracone base. The paracone is both slightly p4 is present, no mental foramen is visible. Additionally, higher and larger than the metacone, and there is no distinct this specimen clearly lacks the small, second mental fora- men beneath the posterior root of p4 seen in some other mesostyle. The metaconule is larger than the protoconule. Wasatchian rodents. The metaloph and protoloph are continuous towards the DP4—UCMP 148675 is identified as a DP4 based on protocone. The hypocone is a large cusp well separated from the expanded anteroloph and narrower lingual portion. both the protocone and metaconule. The posteroloph extends Compared to the molars, the cusp tips are more acute, and around the metacone to the labial margin of the tooth. the lophs are not developed. The paracone is higher than M1/2—Upper first and second molars are square in STRAIT ET AL.—EARLY EOCENE RODENTS FROM WYOMING 11

Table 7. Measurements and descriptive statistics of the dentition Table 8. Measurements and descriptive statistics of the upper preserved in maxillae of Microparamys hunterae from UCMP dentition of Microparamys hunterae from UCMP V71237 and V71237 and V71238, Wasatch Formation, Wyoming. V71238, Wasatch Formation, Wyoming.

M1 M2 P4 M1/M2 M3 L W L W L W L W L W 148611 1.0 1.1 1.1 1.2 148650 0.9 0.9 148638 1.1 1.1 1.2 1.1 148640 1.1 1.2 148639 1.2 1.2 148641 1.2 1.2 148645 1.2 1.2 OR 1.0-1.1 1.1 1.1-1.2 1.1-1.2 148665 1.0 1.1 Mean 1.05 1.10 1.17 1.17 148666 1.1 1.1 SD 0.07 0 0.06 0.06 148667 1.1 1.2 148668 1.2 1.2 occlusal outline with the width typically being equal to, or 148669 - 1.2 only slightly larger than, the length. The protocone has a wider base and is more bulbous than the other cusps. The 148670 1.1 1.1 hypocone is large, equal in height to the metacone, but 148676 1.1 1.0 shorter than the protocone. The hypocone is not connected 148761 1.0 1.0 to the metaconule. The paracone is consistently wider and more robust than the metacone. The paracone is also higher, 148762 1.2 1.2 but this height difference becomes substantially reduced with 148763 1.1 1.1 wear. Both conules are present, and the metaconule is typi- 148766 1.3 1.5 cally slightly larger. The protoconule is slightly anterior to the paracone. Both the protoloph and metaloph are typically 148768 1.1 1.1 discontinuous especially in unworn specimens. The meta- 148769 1.0 1.1 loph is best developed where it extends from metacone to 148647 1.1 1.4 metaconule. The anteroloph extends only along the buccal 148651 1.1 1.2 two-thirds of the tooth. Most specimens have a diminutive mesostyle, which is typically closer to the paracone than 148652 1.3 1.3 metacone. 148653 1.0 1.0 M3—M3 are triangular in occlusal outline and reduced 148642 0.9 0.8 posteriorly with a small, marginally-placed metacone, and hypocone absent. There is a small metaconule which with wear forms a partial metaloph. Anteriorly, the protoconule is OR - - 1.0-1.3 1.0-1.5 - - reduced and incorporated into the protoloph. The mesostyle Mean - - 1.12 1.17 - - is weakly to moderately developed. The anteroloph is similar SD - - 0.09 0.13 - - in design to that of the other molars. Discussion—Microparamys hunterae was previously anterolophid is well developed and is not continuous with only known from UMMP 66968, a fragmentary dentary the protoconid prior to wear; we concur with Ivy’s placement with moderately worn m1-3 (Fig. 7H). This specimen was of this taxon. allocated to Microparamys by Ivy (1990, p. 59) on the basis of Microparamys hunterae occupies the same size range as “the lack of sciuravid lophate characteristics and the presence Knightomys reginensis; however, the Washakie Basin speci- of the diagnostic separation of the anterior cingulum.” Wood mens are morphologically distinct from the K. reginensis (1962, p. 158) noted that separation of the anterolophid from described by Korth (1984) and Flanagan (1986). These speci- the protoconid is a “progressive character, being poorly mens differ from K. reginensis in the following characteristics developed in the Wasatchian forms”, while younger species of the lower molars: complete lack of metastylids; entoconid have a deep valley. Although M. hunterae does not have the is high and columnar and lacks a hypolophid; mesoconid less distinctive valley seen in later-occurring Microparamys, the elongated and does not extend into the talonid basin; and a 12 PALEOBIOS, VOL. 33, FEBRUARY 2016

Table 9. Measurements and descriptive statistics of the dentition preserved in dentaries of Microparamys hunterae from UCMP V71237 and V71238, Wasatch Formation, Wyoming.

p4 m1 m2 m3 L TrW TaW L TrW TaW L TrW TaW L TrW TaW 148610 0.8 0.6 0.7 1.2 0.9 1.0 1.2 1.0 1.2 1.1 1.0 1.0

Table 10. Measurements and descriptive statistics of the lower dentition of Microparamys hunterae from UCMP V71237 and V71238, Wasatch Formation, Wyoming.

p4 m1/m2 m3 L TrW TaW L TrW TaW L TrW TaW 148648 1.2 0.8 0.9 148656 1.0 0.7 0.8 148654 1.2 0.9 1.0 148663 1.1 0.7 0.8 148671 1.1 0.9 0.8 148770 1.4 1.0 1.2 148772 1.2 1.0 1.2 148774 1.3 1.2 1.3 148775 1.2 1.0 1.1 148776 1.3 1.0 1.1 148778 1.2 0.8 1.1 148779 1.2 0.8 0.9 148780 1.3 1.1 1.0 148782 1.4 1.2 1.4 149219 1.2 0.9 1.0 149224 1.2 1.0 1.1 148643 1.2 1.0 1.0 148644 1.3 1.1 1.2 148658 1.3 1.2 1.3 148659 1.3 1.0 1.1 148660 1.2 0.9 1.0 151278 1.4 1.2 1.3 148655 1.1 - 0.8 148771 1.1 0.9 0.8 148777 1.2 1.0 1.0

OR 1.0-1.2 0.7-0.8 0.8-0.9 1.1-1.4 0.7-1.2 0.8-1.4 1.1-1.2 0.9-1.0 0.8-1.0 Mean 1.10 0.75 0.85 1.25 1.00 1.10 1.13 0.95 0.87 SD 0.14 0.07 0.07 0.09 0.14 0.16 0.06 0.07 0.12 STRAIT ET AL.—EARLY EOCENE RODENTS FROM WYOMING 13 complete lack of accessory cuspules in talonid basin. In the upper dentition K. reginensis has a distinctive connection between the hypocone and metaconule (hypoloph), which M. hunterae lacks.

CYLINDRODONTIDAE Miller and Gidley, 1821 Tuscahomys Dawson and Beard, 2007 Tuscahomys ctenodactylops (Korth, 1984) Figs. 8-10, Tables 11-18

Referred specimens—UCMP V71237: UCMP 175197, right dentary with p4, m1-2; UCMP 148615, Rdp4; UCMP 148613, right dentary with p4, m1-3; UCMP 148628, left dentary with m1-3; UCMP 148632,149223, Rm1/2; UCMP 148662, Lm1/2; UCMP 148646, RP3; UCMP 148612, 148624, 148661, right maxillae with P3, M1-3; UCMP 148664, LP3; UCMP 148625, left maxilla with P3, M1-2; UCMP 148616, RP4; UCMP 148673, LP4; UCMP 148626, right maxilla with P4, M1-3; UCMP 148627, left maxilla with M1-2; UCMP 148617-148619, 148636, RM1/2; UCMP 148621, 148622, LM1/2; UCMP 175196, right maxilla with M2-3; UCMP 148633, 148637, RM3; UCMP 148620, 148623, 148635, LM3. UCMP V71238: UCMP 169140, left dentary with p4, m1-3; UCMP 148678, 151320, 152487, Rp4; UCMP 148706, 151321-151324, 151355, Lp4; UCMP 148705, left dentary with m1; UCMP 148746, 171521, right dentaries with m1- 2; UCMP 148677, 148683-148686, 148700, 148707, 148750, Figure 8. Tuscahomys ctenodactylops holotype and paratypes 151344-151354, 151365, 151366, Rm1/2; UCMP 148679- from UW locality V60008. A. UW 15008, holotype left dentary 148682, 148697, 148708, 148710, 151334-151343, 151368, with m1-m2, B. UW 15009, left M1 or M2, C. UW 15263, right 189308, 189310, 235519, 235521, Lm1/2; UCMP 156869, left M1 or M2, D. UW 15262, right P4, E. UW 15010, right maxil- dentary with m1-3; UCMP 151369, left dentary with m2-3; lary fragment with M3. UCMP 148687, 148693, 148695, 148696, 148699, 148709, 148711, 151329-151332, 189307, 235520, Rm3; UCMP on average than T. walshi Anemone, Dawson, and Beard, 148689, 148692, 148694, 148698, 148701-148703, 148753, 2012 and T. worlandensis Rose, Chew, Dunn, Kraus, Fricke, 148754, 151325-151328, 151333, 189309, Lm3; UCMP and Zack, 2012. Differs from T. medius in having a slightly 151318, 189313, DP4; UCMP 152485, left maxilla with P3-4; higher crowned cheek teeth. Differs from T. medius and T. UCMP 189314, RP3; UCMP 152484, LP3; UCMP 148715, minor in having a larger M3 metaconule. Differs from T. 151315, 151316, 151356, 189312, RP4; UCMP 148722, walshi in having relatively narrower posterior molars and 148723, 148727, 148729, 151311-151314, 189315, LP4; a smaller M3. UCMP 148712-148714, 148721, 148728, 148730, 148734, Description—Korth (1984) described Tuscahomys (for- 148736, 148737, 148739, 148742, 148745, 151301-151310, merly Reithroparamys) ctenodactylops from a left dentary 189302 RM1/2; UCMP 148716-148718, 148724-148726, with m1-m2, an isolated P4, and 3 upper molars from a 148732, 148733, 148735, 148740, 148744, 151293-151300, University of Wyoming locality from near the base of the 151317, 151367, 152486, 189306, LM1/2; UCMP 148738, Wasatch Formation in the Washakie Basin and at approxi- 148764, 148767, 151279-151284, 189303, RM3; UCMP mately the same stratigraphic level as and quite near Roehler’s 148719, 148741, 148743, 151285-151292, 189300, LM3. Emended Diagnosis—Differs fromT . minor Dawson Coryphodon Catastrophe Quarry (McGee 2001). Based on and Beard, 2007 and T. medius Dawson and Beard, 2007 in the geographic position of the type locality, it lies near the larger size, is comparable in size to T. major, and is smaller base of Roehler’s (1993) master section for the Main Body 14 PALEOBIOS, VOL. 33, FEBRUARY 2016

Figure 9. Tuscahomys ctenodactylops from UCMP loc. V71237. A. UCMP 148612, right maxilla with P3-M3, B. UCMP 148664, right P3, C. UCMP 148613, right dentary with p4-m3. Scale bar = 1 mm. of the Wasatch Formation and is at approximately the same with the original illustrations was inaccurate. We also in- stratigraphic level as V71237 and V71238 with respect to clude illustrations of the original sample (Fig. 8) as well as the base of the formation. This large collection of specimens exemplars from the collections described here (Figs. 9-10). from V71237 and V71238 provides us with the opportunity dP4—These deciduous teeth are heart-shaped, with a nar- to describe all cheek tooth positions, examine individual rower lingual portion. Compared to the permanent teeth, the cusp and conule tips are more acute, and lophs are not variation, and expand its diagnosis. We have also included developed. The cingulum is discontinuous buccally due to measurements of the holotype (UW 15008) and paratypes, as wear. A minute mesostyle is variably present. There is a small measurements were not explicitly provided in Korth (1984), hypocone, and the hypocone and protocone are more closely and our measurements indicate that the scale bar associated appressed than in the molars. STRAIT ET AL.—EARLY EOCENE RODENTS FROM WYOMING 15

Figure 10. Tuscahomys ctenodactylops. A. UCMP 148613, right dentary in lateral view, B, C. UCMP 169140, left dentary in lateral and medial views, D, E. UW 15008, holotypes left dentary in lateral and medial view.

P3—P3 is known from four maxillary specimens and two P4—The paracone and metacone are subequal and slightly isolated teeth. This tooth position shows extreme variability. anteroposteriorly compressed. Korth (1984) stated that the Root number varies from one to two and the unworn crowns metacone is slightly more buccal than the paracone, but we vary and can include one primary cusp, one primary cusp find that this orientation is variable. The metaconule is much with a smaller accessory cusp, or two relatively equally size larger than the protoconule. Two of the 10 specimens (UCMP cusps. With wear P3 looks simple and peg-like. 148673, 148723) have a mesostyle. All cusps are bulbous and 16 PALEOBIOS, VOL. 33, FEBRUARY 2016

Table 11. Measurements and descriptive statistics of the dentition preserved in maxillae of Tuscahomys ctenodactylops from UCMP V71237 and V71238, Wasatch Formation, Wyoming.

P3 P4 M1 M2 M3 L W L W L W L W L W 152485 0.7 0.8 1.1 1.2 1.7 1.7 148625 0.9 1.0 1.7 2.3 2.0 2.6 2.0 2.3 148612 0.9 1.0 1.6 2.0 2.0 2.3 2.1 2.4 1.9 1.9 148624 1.0 1.4 1.8 2.2 2.0 2.3 2.0 2.3 2.2 2.1 148661 0.8 1.0 1.8 2.4 2.0 2.6 2.0 2.6 2.1 2.1 148626 1.6 1.8 1.8 2.2 1.8 2.0 148627 1.9 2.3 2.0 2.3 175196 2.0 2.5 2.1 2.2

OR 0.7-1.0 0.8-1.4 1.1-1.8 1.2-2.4 1.7-2.0 1.7-2.6 1.8-2.1 2.0-2.6 1.9-2.2 1.9-2.2 Mean 0.86 1.04 1.60 1.98 1.91 2.29 1.99 2.34 2.08 2.08 SD 0.11 0.22 0.26 0.44 0.12 0.30 0.09 0.19 0.13 0.13 protoloph and metaloph develop with wear. In most cases the relative to the talonid. The metaconid is much larger than slight buccal cingulum is restricted to the area between the the protoconid, but does not show the anteroposterior com- paracone and metacone. However, in a few specimens (e.g., pression or obliquity characteristic of the permanent cheek UCMP 148612, 148625, 148722, and 148729) this cingulum teeth. An anteroconid and metalophulid II are present. An is continuous with both the anteroloph and posteroloph. The ectolophid and hypolophid are both present. In permanent hypocone is very small (even smaller than the metaconule), teeth, the hypoconid and entoconid are comparable in size; and is only separated from the protocone by a slight groove. however, in the dp4 the hypoconid is high and columnar; M1/2 and M3—Molars are as described by Korth (1984), the entoconid and hypoconulid are smaller and confluent with the following additional observations. M1/2 are narrow with the posterolophid. teeth, with the width being greater than the length. In M3 p4—These are the first known p4s of this species. The trigonid is dominated by an enlarged metaconid which is the length and width measurements are essentially equal. equal in size to the m1 metaconid. The shorter and narrower In M1/2 mesostyles are variable in their development, even protoconid is labial to the mid-line and closely oppressed to within the same tooth row (e.g., UCMP 148626). The co- the metaconid, but separated from it by a v-shaped valley. nules are relatively large, but the metaconule is wider than With slight-medium wear the metalophulid II descends from the more anteroposteriorly compressed protoconule. The the posterolingual corner of the protoconid and terminates hypocone and protocone are relatively internal, resulting in posterior to the metaconid at the midline of the cusp. The a sloped appearance to the crown lingual to these cusps. On mesoconid is small and round, located immediately poste- maxillae having both M1 and M2, there is little difference rior to the protoconid. Ectolophids only develop with wear. in morphology. The only consistent difference is that the The bulbous hypoconid is wider, but not higher, than the lingual slope is steeper and the tooth is absolutely wider in entoconid. The entoconid is isolated from the posterolophid, M1 than M2. Korth (1984) reported the metacone of M3 to which with wear connects the hypoconulid to the hypoconid. be absent, but some specimens in our sample (e.g., UCMP The hypoconulid is centrally positioned, anteroposteriorly 148637) retain very small metacones. Additionally, on M3 compressed, and is more lophate than cuspidate. A short the presence of a minute hypocone is variable and they lack crest arises from the base of the entoconid and is directed a distinctive mesostyle. toward the hypoconulid but does not meet it. This crest is dp4—UCMP 148615 is the sole deciduous premolar of not apparent in worn specimens. this taxon and is slightly smaller than the permanent pre- m1/2—The trigonid is moderately higher than the talonid. molars. It is a molariform teeth with a very narrow trigonid In unworn specimens the metaconid is markedly higher and STRAIT ET AL.—EARLY EOCENE RODENTS FROM WYOMING 17

Table 12. Measurements and descriptive statistics of the upper of the hypoconid. The rounded mesoconid is positioned premolars of Tuscahomys ctenodactylops from UCMP localities just labial of the midline and posterior to the protoconid, V71237 and V71238, Wasatch Formation, Wyoming, and from leaving a shelf-like area immediately labial to it. In some UW locality V6008, Wasatch Formation, Wyoming. Note that specimens this shelf is enclosed by a buccal cingulid. A the observed range, mean, and standard deviation exclude UW hypolophid is consistently present and is typically directed 15262. from the entoconid toward the mesoconid. In some cases, P3 P4 this crest connects with the mesoconid. Hypoconulids are elongated and lophate, connected to the larger hypoconid by L W L W a continuous protolophid and separate from the entoconid. 148646 0.7 0.9 Although Korth (1984) stated that m1 is smaller than m2, it is not possible to distinguish isolated teeth due to the amount 148664 1.0 0.7 of variability present in the sample. 152484 1.1 1.4 m3—The third molar has not previously been reported. 148616 1.8 2.5 The third molar is similar to m1-m2 in form, except the talonid is subequal to or narrower than the trigonid. The 148673 2.0 2.5 hypoconulid is more posteriorly positioned, higher, and 148715 1.6 2.3 connected to both entoconid and hypoconid. The hypolo- 148722 1.6 2.4 phid is obliquely oriented and with wear this crest joins the mesoconid. 148723 1.9 2.6 Dentary—All three specimens that preserve this area 148727 1.7 2.4 (UCMP 148613, 148628, and 148705) bear two mental fo- 148729 1.5 2.0 ramina: one larger foramen beneath the anterior root of p4 151311 1.7 2.1 and a second smaller foramen beneath the posterior root of p4. The dentary is best preserved in UCMP 148613 and 151312 1.6 2.2 169140 (Fig. 10). The dentary is deep relative to the height 151313 1.6 2.3 of the teeth. The diastema between the p4 and incisor is 151315 1.8 2.3 short and has a sharply defined ridge. Two mental foramina are present. The anterior foramen is larger, more oval and 151316 1.6 2.1 located beneath the anterior root of p4, approximately at 151317 2.0 2.4 half the height of the dentary. The smaller mental foramen 151356 1.6 2.6 is circular and slightly ventral and posterior to the former, occurring under the posterior root of p4. The masseteric 189312 2.0 2.6 fossa is deeply excavated and delineated by rounded ridges 189313 2.0 3.0 coming down from the coronoid process of ascending ramus 189315 1.6 2.4 and forward from the angular process. A small protuberance is present at the anteriormost point where the ridges meet, UW 15262 1.8 2.7 beneath m2. The angular process of the dentary is broken, but the base of it shows that it would have extended ventrally as OR 0.7-1.1 0.7-1.4 1.5-2.0 2.0-3.0 well as posteriorly. The ventral border of the angular process Mean 0.93 1.00 1.74 2.39 shows striations for muscle attachments. On the lingual side the pterygoid fossa is posteroventral to the m3. The labial SD 0.21 0.36 0.18 0.24 side is convex, whereas the lingual side is too damaged to its base is slightly wider than the protoconid. The metaconid determine if it was concave or flattened. The symphyseal is positioned marginally and slightly obliquely oriented, but surface is lightly rugose and extends posteriorly only to a the protoconid is angled more lingually. Both anterolophid spot slightly anterior to p4. Discussion—Originally described by Korth (1984) as a and metalophulid II are present, but their expression var- ies. The mesoconids are large, filling the space between the species of Reithroparamys, Dawson and Beard (2007) reas- protoconid and hypoconid. In some unworn teeth (e.g., signed this species to the genus Tuscahomys. Based on our ex- UCMP 148700) a very slight ectolophid is visible. However, panded sample of this species, we have included an emended early in wear the ectolophid disappears, and the mesoconid diagnosis of T. ctenodactylops above. This diagnosis does not eventually becomes confluent with the anterolingual edge include many of the characters that have previously appeared 18 PALEOBIOS, VOL. 33, FEBRUARY 2016

Table 13. Measurements and descriptive statistics of the upper M1 or M2 of Tuscahomys ctenodactylops from UCMP localities V71237 and V71238, Wasatch Formation, Wyoming and from UW locality V6008, Wasatch Formation, Wyoming. Note that the ob- served range, mean, and standard deviation exclude UW 15009 and 15263. M1/M2 M1/M2 L W L W 148617 2.0 2.3 151295 2.1 2.1 148618 2.1 2.3 151296 2.0 2.2 148619 2.0 2.5 151297 2.1 2.1 148621 2.0 2.2 151298 1.9 2.2 148636 2.0 2.6 151299 2.0 2.1 148714 2.0 2.6 151300 2.0 2.1 148716 2.0 2.5 151301 1.9 2.2 148717 1.9 2.0 151302 2.0 2.3 148718 - 1.9 151303 2.0 2.4 148721 2.0 2.5 151304 2.0 2.2 148724 2.1 2.2 151305 2.0 2.1 148725 2.0 2.4 115306 2.0 2.3 148726 1.8 2.6 115307 2.0 2.3 148728 1.9 2.1 115308 2.0 2.3 148730 2.0 2.0 151309 2.2 2.4 148732 2.1 2.7 151310 1.9 2.1 148733 2.1 2.1 151367 2.0 2.3 148734 2.1 2.7 189302 2.2 2.5 148735 2.0 2.2 189306 1.8 2.9 148736 2.2 2.4 235522 2.0 2.3 148739 1.9 2.4 UW 15009 2.1 2.6 148740 1.9 - UW 15263 2.1 2.8 148742 2.0 2.0 148744 2.0 2.0 OR 1.8-2.2 1.9-2.9 151293 2.0 2.3 Mean 2.00 2.29 151294 1.9 2.3 SD 0.09 0.22

in diagnoses for other species of Tuscahomys, including P4 The lower molars of the holotype and the upper molars in- protocone position, upper cheek tooth anterior cingulum cluded in the type series fall within the range of metric and development, and relative protoconule size (see Dawson morphological variation seen in the V71237 and V71238 and Beard 2007), talonid width, entoconid height, and cusp samples. However, the P4 described by Korth (1984) (UW isolation (see Anemone et al. 2012), and P4 hypocone size/ 15262) is larger than any of the specimens from V71237 presence (see Rose et al. 2012). These characters are too and V71238 and falls within the size range of Tuscahomys variable and/or too difficult to reliably quantify within our walshi. The crown is more rectangular rather than squarish, sample and easily erased with wear. and the ectocingula is not continuous across the labial side Comparisons of our samples to the holotype and the four of the tooth, but is discontinuous labial to the metacone. specimens of the hypodigm (Fig. 8) reveal several differences. The central trough is deeper and separates the paracone and STRAIT ET AL.—EARLY EOCENE RODENTS FROM WYOMING 19

Table 14. Measurements and descriptive statistics of the upper metacone, and both conules and the hypocone are better M3 of Tuscahomys ctenodactylops from UCMP V71237 and developed and more inflated at their bases. In all these fea- V71238, Wasatch Formation, Wyoming, and from UW V6008, tures, the P4 ascribed to the type series of T. ctenodactylops Wasatch Formation, Wyoming. Note that the observed range, resembles T. walshi. mean, and standard deviation exclude UW 15010. While Tuscahomys minor, T. medius, and T. worlandensis M3 can be readily differentiated from T. ctenodactylops based on size, separating T. major and T. walshi from T. ctenodactylops L W is more difficult, as these overlap in size. Tuscahomys major 148620 2.0 2.0 is currently known from 10 specimens that document the 148622 1.8 2.3 following tooth positions: DP4, P4, M1 or M2, and m2 (Daw- 148623 2.0 2.0 son and Beard 2007, Beard and Dawson 2009). Comparing T. major with our measurements of the enlarged sample of 148633 2.2 2.2 T. ctenodactylops, T. major teeth fall within the range of T. 148635 2.0 2.0 ctenodactylops for m2, P4, and the type sample of M1 or M2. 148637 1.9 1.8 They differ by less than a tenth of a millimeter for DP4, and 148719 2.1 2.2 the only notably different tooth is the very wide M1 or M2 148738 2.0 2.1 referred to T. major after its initial description (CM 81754; Beard and Dawson 2009). Dawson and Beard’s (2007) only 148741 2.1 - morphological character differentiating T. major and T. 148743 2.0 2.1 ctenodactylops is P4 metaconule size. The P4 of T. major 148764 2.0 2.0 are worn and variation for this character is not known. 148767 2.0 1.9 The only other possible morphological difference between 151279 2.2 2.1 these similarly-sized species may be more consistent pres- ence of mesostyles in T. major. This variation in mesostyle 151280 2.0 2.0 size and the limited size differences may not be sufficient 151281 2.0 2.1 to distinguish T. major from the expanded sample of T. 151282 2.1 2.0 ctenodactylops. 151283 2.1 2.1 By contrast, Tuscahomys walshi can be more readily dif- 151284 2.1 2.1 ferentiated from T. ctenodactylops based on selected dental characters (see diagnosis), but there is overlap in the size 151285 2.0 2.0 ranges for these two species. Although it is easy to look at 151286 2.0 2.0 these assemblages from limited stratigraphic and geographic 151287 2.2 2.1 ranges and detect the differences between T. ctenodactylops 151288 2.1 2.1 and T. walshi, identifying specimens from other areas and/ 151289 2.2 2.2 or which are only represented by selected isolated teeth is likely to be challenging. Additionally, the existence of both 151290 2.1 2.1 species in the same geographic basin and at different times 151291 2.1 2.0 also suggests the possibility that these represent lineage- 151292 2.1 2.0 segments (sensu de Queiroz 1998, 1999) and future work 189300 1.8 1.9 may find them to be taxonomically indistinct. 189303 2.2 2.1 SCIURAVIDAE (Miller and Gidley, 1918) UW 15010 2.0 2.0 Knightomys Gazin, 1962 Knightomys cf. K. minor Ivy, 1990 OR 1.8-2.2 1.8-2.3 Fig. 11; Table 19

Mean 2.05 2.06 Referred specimens—UCMP V71237: UCMP 148657, SD 0.11 0.11 Rm3; UCMP 148649, LM1/2. 20 PALEOBIOS, VOL. 33, FEBRUARY 2016

Table 15. Measurements and descriptive statistics of the dentition preserved in dentaries of Tuscahomys ctenodactylops from UCMP localities V71237 and V71238, Wasatch Formation, Wyoming, and the holotype from UW locality V6008, Wasatch Formation, Wyoming. Note that the observed range, mean, and standard deviation exclude UW 15008.

p4 m1 m2 m3 L TrW TaW L TrW TaW L TrW TaW L TrW TaW 175197 1.9 1.3 1.4 2.2 1.7 1.9 2.2 1.9 2.1 148613 1.9 1.2 1.5 1.9 1.4 1.7 2.0 1.7 1.9 2.4 1.6 1.6 169140 1.8 1.3 1.5 1.9 1.4 1.7 2.0 1.7 1.9 2.5 1.7 1.7 148705 2.0 1.7 1.9 148746 2.3 1.6 1.9 2.4 1.8 2.0 171521 2.0 1.6 1.8 2.1 1.8 2.0 148628 1.8 1.5 1.7 2.0 1.8 1.9 2.4 1.8 1.6 156869 2.1 1.6 1.9 2.3 2.0 2.1 151369 2.2 1.8 1.9 - 1.8 - UW 15008 2.1 1.5 1.8 2.3 1.8 2.0

OR 1.8-1.9 1.2-1.3 1.4-1.5 1.8-2.3 1.4-1.7 1.7-1.9 2.0-2.4 1.7-2.0 1.9-2.1 2.4-2.5 1.6-1.8 1.6-1.7 Mean 1.87 1.27 1.47 2.03 1.56 1.81 2.15 1.81 1.96 2.43 1.73 1.63 SD 0.06 0.06 0.06 0.17 0.12 0.10 0.15 0.10 0.09 0.06 0.10 0.06

Table 16. Measurements and descriptive statistics of the lower premolars of Tuscahomys ctenodactylops from UCMP V71237 and V71238, Wasatch Formation, Wyoming.

p4 L TrW TaW 148678 1.4 1.6 - 148706 2.0 1.5 1.6 151320 2.0 1.4 1.7 151321 2.0 1.4 1.7 151322 1.9 1.4 1.7 151323 1.9 1.4 1.6 Figure 11. Knightomys cf. K. minor. A. V71237/148649, left 151324 2.0 1.3 1.6 M1/2, B. V71237/148657, right m3. 151355 1.9 1.4 2.1 151487 1.9 1.3 1.5 UCMP V71238: UCMP 148781, Rdp4; UCMP 148765, LP4. OR 1.4-2.0 1.3-1.6 1.5-2.1 Description—P4—The P4 is an anteroposteriorly short tooth dominated by lophs. The protocone is rounded and the Mean 1.89 1.41 1.69 protoloph and metaloph are continuous towards this cusp. SD 0.19 0.09 0.18 The anteroloph is relatively small, whereas the posteroloph is shelf-like and the hypocone is incorporated as a small bulge at its lingual end. The paracone and metacone, although STRAIT ET AL.—EARLY EOCENE RODENTS FROM WYOMING 21

Table 17. Measurements and descriptive statistics of the lower m1 or m2 of Tuscahomys ctenodactylops from UCMP V71237 and V71238, Wasatch Formation, Wyoming.

m1/m2 m1/m2 L TrW TaW L TrW TaW 148632 2.3 1.9 2.0 151341 2.1 1.8 1.9 148662 2.2 1.9 2.0 151342 1.8 1.4 2.0 148677 2.2 1.5 1.8 151343 2.0 1.6 1.7 148679 2.0 1.6 1.8 151344 2.2 1.8 1.9 148680 2.2 1.9 2.0 151345 2.1 1.6 2.1 148681 2.1 1.9 2.2 151346 2.0 1.8 2.0 148682 2.2 1.7 2.0 151347 2.0 1.6 2.0 148683 2.2 1.8 1.7 151348 2.1 1.6 1.9 148684 2.1 1.6 1.8 151349 2.3 1.9 1.9 148685 2.3 2.1 - 151350 2.3 1.9 2.0 148697 2.2 1.9 2.1 151351 2.0 1.6 2.1 148700 2.2 2.0 2.2 151352 2.2 1.9 1.9 148707 2.2 1.9 1.9 151353 2.1 - 2.0 148708 2.3 1.9 1.9 151354 2.3 2.0 - 148710 2.1 1.5 1.8 151365 2.1 1.7 - 148750 2.3 2.1 2.2 151366 2.0 1.8 2.0 149223 2.1 2.2 2.2 151368 2.1 1.6 1.8 151334 2.0 1.5 1.7 189310 2.2 1.9 2.0 151335 2.1 1.5 1.7 235519 - 1.6 - 151336 2.2 1.6 1.7 235521 2.4 1.8 - 151337 2.0 1.6 1.9 151338 2.3 1.6 1.8 OR 1.8-2.4 1.4-2.2 1.7-2.2 151339 2.3 1.9 1.7 Mean 2.16 1.76 1.93 151340 2.3 1.6 2.0 SD 0.12 0.19 0.15 broken, are closely appressed and there is no evidence of a centrally-positioned anteroconid and labio-lingually aligned buccal cingulum. protoconid and metaconid. The trigonid is narrower than M1/2—Although the upper molar is in the same size range the open, wide talonid basin. The metaconid is higher and as the specimens of Microparamys from these localities, it dif- slightly larger than the protoconid. No metalophulids are fers significantly from them in that there is a distinct connect present, and the protoconid and metaconid are separated by a from the hypocone to the metaconule, typical of Knightomys. distinct valley. A slight but distinct ectolophid is present, but This specimen also has a double metaconule, protoconule a mesoconid is absent. The talonid is longer than the trigonid anteriorly displaced, and a mesostyle connected to paracone with labio-lingually aligned entoconid and hypoconid. No by faint crest. The metacone is higher than the paracone. hypolophid is present, but the entoconid, hypoconid, and dp4—Based on size and morphology UCMP 148781 small centrally-positioned hypoconulid are joined by a low is tentatively identified as Knightomys. This tooth has posterolophid. typical deciduous characteristics including thinner enamel, m3—The m3 is moderately worn. The trigonid is only splayed roots, and trigonid composed of a small, isolated slightly higher than the talonid. There is a small trigonid 22 PALEOBIOS, VOL. 33, FEBRUARY 2016

Table 18. Measurements and descriptive statistics of the lower Table 19. Measurements and descriptive statistics of the den- m3 of Tuscahomys ctenodactylops from UCMP V71237 and tition of Knightomys cf. K. minor from UCMP V71237 and V71238, Wasatch Formation, Wyoming. V71238, Wasatch Formation, Wyoming.

m3 m3 P4 M2 L TrW TaW L TrW TaW L W L W 148687 - - 2.0 148657 1.4 1.2 1.1 148689 2.6 1.8 1.7 148765 1.0 1.2 148692 2.3 1.7 1.6 148649 1.2 1.3

148693 2.8 1.9 1.9 posterolophid by a shallow valley and the basin is lingually 148694 2.5 1.9 1.8 open. The hypoconid is bulbous and continuous with the 148695 2.6 1.9 1.8 posterolophid. No distinct hypoconulid is present. Discussion—These teeth are in the size range for bothK . 148696 2.8 1.8 1.9 minor and K. cremneus Ivy, 1990. They are assigned to K. cf. 148698 2.7 1.9 1.8 K. minor based on lower molar distinctions from K. cremneus 148699 2.5 1.8 1.7 including: a much smaller posteroloph and less bunodont cusps, metalophulid II comprising only the 148701 2.8 1.8 1.7 protoconid arm, and open talonid basin. 148702 2.5 1.8 1.7 148703 2.6 1.8 1.7 DISCUSSION 148709 2.5 1.5 1.5 The presence of massive sandstone units within this por- tion of the Wasatch Formation suggests an active floodplain 148711 - - 1.6 environment in which catastrophic flooding may have had 148753 2.6 1.8 1.7 an impact on the terrestrial communities. This inference is 148754 2.5 1.8 1.8 supported by the presence of two catastrophic assemblages within the lowermost 40 meters of the formation, including 151325 2.5 1.7 1.7 UCMP V71237 (Lower Meniscotherium) as well as UCMP 151326 2.4 1.7 1.5 V72193 (Roehler’s Coryphodon Catastrophe Quarry) 151327 2.7 1.8 1.6 (Roehler 1993, McGee 2001). Based on the limited degree of disarticulation, Williamson (2001) inferred that the 151328 2.4 1.7 1.6 remains of Meniscotherium tapiacetum in UCMP V71237 151329 2.7 2.0 1.7 were buried very shortly after death, likely within a matter 151330 2.6 1.7 1.9 of weeks, during a single fluvial event. Williamson (2001) further noted that the absence of smaller skeletal elements 151331 2.7 1.9 1.5 of Meniscotherium in the assemblage suggested that it was a 151332 - - 1.8 winnowed assemblage that had undergone limited transport. 151333 2.5 1.9 1.6 UCMP V71238 is a channel lag assemblage, typical of many 189309 2.6 1.9 1.8 vertebrate accumulations that occur in the fossil record. Given the unique depositional history of UCMP V71237, we can hypothesize that it may more accurately reflect the OR 2.3-2.8 1.5-2.0 1.5-2.0 composition of the local early Eocene mammalian com- M 2.58 1.80 1.72 munity than assemblages that accumulated as the result of more active fluvial processes. SD 0.13 0.11 0.13 To assess rodent assemblage composition and the extent basin delimited by both metalophulids I and II. There is a very to which the rodents from these two sites may reflect the small mesostylid in the valley between the metaconid and composition of the original mammalian community, we entoconid. The mesoconid is slightly lingual to the midline calculated total number of specimens (TNS) and minimum of the protoconid and hypoconid and extends as a low loph number of individuals (MNI) for each of the rodent taxa into the talonid basin. The entoconid is separated from the based on counts of the cheek teeth (Table 20). Additionally, STRAIT ET AL.—EARLY EOCENE RODENTS FROM WYOMING 23

Table 20. Summary of total number of specimens (TNS) and minimum number of individuals (MNI) from each locality.

UCMP V71237 UCMP V71238 Species TNS MNI TNS MNI Paramys copei 0 0 1 1 P. taurus 7 2 19 5 Lophiparamys murinus 4 1 6 3 Microparamys hunterae 34 2 20 2 Tuscahomys ctenodactylops 33 5 171 18 Knightomys cf. K. minor 2 1 1 1 we calculated the TNS of all mammalian taxa from each described. The only rodent assemblages of comparable age to quarry, using only the last two premolars and molars to the UCMP V71237 and V71238 are those from early Wasat- generate values comparable to those of rodents. The TNS chian (Wa3, early Graybullian) localities from the Clarks of mammals from UCMP V71237 is 397, with 78 of these Fork Basin described by Ivy (1990). The Clarks Fork Basin as- representing rodents (i.e., 19.6% of the total fauna). Within semblages are dominated by Acritoparamys atwateri (Loomis, UCMP V71238, the TNS of mammals is 1101, with rodents 1907) and Paramys taurus, with rarer appearances of P. copei, (n=196) representing 17.8%. These relative percentages for P. pycnus Ivy, 1990, Microparamys cheradius, Lophiparamys rodents based on TNS are comparable to values reported murinus, Knightomys cremneus, and Reithroparamys cf. R. for Wasatchian quarries in the Bighorn Basin (Silcox and debequensis Wood, 1962. As noted by Ivy (1990), the rarity of Rose 2001, Strait 2001) and Four Mile fauna of northwestern smaller rodents (e.g., P. pycnus, M. cheradius, and L. murinus) Colorado (Bown 1979) and are significantly higher than is likely the result of the assemblages being almost entirely those from Bighorn Basin surface collections, where rodents comprised of surface collections, a collecting technique that generally represent less than 10% of fossils recovered (Bown is known to undersample smaller specimens. 1979, Clyde 1997, Silcox and Rose 2001). Although UCMP In a slightly older, earliest Wasatchian (Wa0) screen- V71237 is unusual in having a relatively high proportion of washed site from the southeastern Bighorn Basin, Strait the rare condylarthran Meniscotherium, representing 27.7% (2001) reported Acritoparamys atwateri as the dominant of TNS, it appears that the relative abundance of rodents taxon, with rarer occurrences of Paramys taurus and P. copei. within the fauna as a whole is comparable to that known from Expanded samples have revealed that many of the specimens other quarried or screen-washed Wasatchian sites. That the previously identified as A. atwateri represent a new species relative abundances of rodents in quarried or screen-washed near Tuscahomys and that this taxon is the dominant rodent Wasatchian localities falls generally between 13-20% of TNS (Strait 2006) within this assemblage; this taxon is also now strongly suggests that these values accurately reflect the known to be the dominant rodent in other earliest Wasat- abundances of these animals on the Eocene landscape and chian sites (Gingerich and Smith 2006, Rose et al. 2012). highlights their importance in these ecosystems. In the central Bighorn Basin where somewhat younger, Examination of the TNS and MNI data (Fig. 12) for middle Wasatchian (Wa4 and Wa5) quarries have produced abundant rodents (see Silcox and Rose 2001), Paramys cf. P. individual rodent taxa reveals that the dominant taxa at taurus is frequently the most common taxon, with the single UCMP V71237 and V71238 are Tuscahomys ctenodactylops exception being within the rodent fauna from the McNeil and Microparamys hunterae, although at a gross level their Quarry, where Knightomys sp. dominates. In these faunas, abundances differ significantly between the two levels, and Knightomys is otherwise a less common element, as are cf. whether TNS or MNI is employed. Paramys taurus and Acritoparamys atwateri and cf. P. copei. A number of other Lophiparamys murinus are the next most abundant, and rodent taxa have been reported from the mid-Wasatchian Knightomys cf. K. minor and P. copei make up a minor part (Wa3-5; Graybullian) of the Bighorn Basin (see Wood 1962, of the fauna, with P. copei absent from UCMP V71237. Korth 1984), but all of these are based on only a single fossil or just a handful of specimens from unknown stratigraphic Comparison with other early Wasatchian rodent horizons. Within the Greater Green River Basin, Tuscahomys assemblages is extremely abundant at the slightly younger (Wa4) Smiley Although rodents are fairly common at many early Eo- Draw locality where it co-occurs with two additional, un- cene sites, few rodent assemblages have been systematically specified rodent taxa (Anemone et al. 2012). 24 PALEOBIOS, VOL. 33, FEBRUARY 2016

Graybullian to Lysitean screen-washed assemblages from Knightomys cf. K. minor the San Jose Formation in New Mexico, Apatosciuravus, Tuscahomys ctenodactylops Mattimys Korth, 1984, and Pauromys spp. are present in the Microparamys hunterae southern fauna, but are absent in the Washakie and Bighorn V71238 Lophiparamys murinus Basin samples, although Korth (1984) has reported the oc- V71237 currence of Apatosciuravus from unspecified localities in Paramys taurus the Bighorn Basin and from the Four Mile fauna. Paramys P. copei copei is shared among all three of these basins, and slightly 0 5 10 15 20 younger species of Paramys, Knightomys, and Lophiparamys Minimum Number of Individuals (MNI) are all present. This brief summary of rodent distributions highlights sev- Knightomys cf. K. minor eral aspects of early Eocene biogeography. The rodent faunas

Tuscahomys ctenodactylops of the Western Interior (where reported to date) all share the common taxa Paramys copei and P. taur u s and species Microparamys hunterae of Microparamys. Even rare taxa, i.e., Lophiparamys muri- Lophiparamys murinus V71238 V71237 nus and the genus Knightomys, appear to be geographically

Paramys taurus widespread in the western United States. Not surprisingly, the greatest similarity of the V71237 and V71238 assemblages P. copei is with the nearby Smiley Draw local fauna (Anemone et al., 0 20 40 60 80 100 120 140 160 180 2012). What is less expected is the similarity of V71237 and Total Number of Specimens (TNS) V71238 to Wa0 assemblages in both the Bighorn Basin and Mississippi, specifically in the presence and dominance of Figure 12. Relative abundance of rodents from UCMP V71237 Tuscahomys species. Anemone et al. (2012) suggested that and V71238 based on total number of specimens (TNS) and Tuscahomys was part of a suite of commonly co-occurring minimum number of individuals (MNI). taxa that include Meniscotherium that may characterize a Despite the differences in collecting methodologies distinct ecotype. We concur that this is one possible explana- between these assemblages and the limited number of re- tion for these distributions; however, we are more cautious ported rodent occurrences, there are nonetheless notable and in our interpretations. Meniscotherium occurs in many lo- measurable differences in the composition of the Wasatchian calities and has a broad geographic range (Williamson and faunas from Wyoming. In particular, Acritoparamys is ab- Lucas, 1992), and we have very incomplete knowledge of sent in the Washakie Basin localities, and Tuscahomys and what taxa consistently co-occur with it throughout its range. Microparamys are the dominant taxa in UCMP V71237 and The hypothesis that Meniscotherium and Tuscahomys co- V71238 but rare in the Clarks Fork and central Bighorn Basin occurrences can be used as ecological indicators is certainly samples younger than Wa0. Knightomys also appears to be somewhat more common in the stratigraphically younger suggested by current data, but we feel this hypothesis needs Bighorn Basin quarries than in the Washakie Basin sample additional faunal data to be rigorously tested. presented here. More geographically distant areas show greater dissimilar- SUMMARY ity to the Washakie Basin rodents. Whereas the Wa0 fauna Here, we comprehensively described the rodent fauna from the Tuscahoma Formation in Mississippi is dominated from UCMP V71237 and V71238 (Lower and Upper Me- by Tuscahomys, with the genus represented by three species, niscotherium), two stratigraphically closely spaced but sedi- the remainder of the rodent fauna is comprised of five mem- mentologically and taphonomically distinct localities in the bers of the Paramyidae, including one species of Paramys, a Main Body of the Wasatch Formation of early Wasatchian species questionably referable to Franimys Wood, 1962, a spe- (Wa3) age from the Washakie Basin of Wyoming. Notable cies otherwise only known from Europe (Corbarimys Maran- occurrences include representatives of Lophiparamys, dat, 1989), and another two undetermined species (Dawson Knightomys, Paramys taurus and P. copei. Additionally, and Beard 2007, Beard and Dawson 2009). Other families of these assemblages include some of the best preserved, most rodents are not yet known from there. Comparing the UCMP complete specimens of Tuscahomys ctenodactylops and V71237 and V71238 assemblages with Flanagan’s (1986) late Microparamys hunterae described to date and which add STRAIT ET AL.—EARLY EOCENE RODENTS FROM WYOMING 25 considerable new morphologic information. Counts of Batsch, A. J. G. C. 1788. Versuch einer Anleitung, zur Kenntiβ specimens reveal that Tuscahomys is the most abundant taxon und Geschicte der Thiere und Mineralien. Akademische Buch- in both localities and that Microparamys is notably under- handlung, Jena. 528 pp. represented in UCMP V71238 relative to the occurrence of Beard, K. C. and M. R. Dawson. 2009. Early Wasatchian mammals this taxon within UCMP V71237, a likely taphonomic size of the Red Hot local fauna, uppermost Tuscahoma Formation, Lauderdale County, Mississippi. Annals of Carnegie Museum bias resulting from depositional differences. 78:193-243. Comparison with other Wasatchian assemblages dem- Benton, M. J. and J. M. Clark. 1988. Archosaur phylogeny and the onstrates that these two Washakie Basin assemblages differ relationships of the Crocodylia. Pp. 295–338 in M. J. Benton considerably from those recovered from contemporaneous (ed.). The Phylogeny and Classification of the Tetrapods. Vol- and slightly younger assemblages within the more northerly ume 1: Amphibians, Reptiles, Birds. Clarendon Press, Oxford. Willwood Formation. The rodent fauna from UCMP V71237 Bonaparte, C. L. 1838. Selachorum tabula analytica. Nouvelles An- and V71238 is also notably different from the stratigraphi- nales des Sciences Naturelle 2. cally younger faunas of the Wind River and San Jose for- Bowdich, T. E. 1821. An analysis of the natural classifications mations. Somewhat surprisingly, however, the fauna from of Mammalia for the use of students and travellers. J. Smith, Paris. 115 pp. these two localities shares some elements not only with the Bown, T.M. 1979. Geology and mammalian paleontology of the geographically close but slightly younger, middle Wasatchian Sand Creek facies, lower Willwood Formation (lower Eocene), (Wa4) Smiley Draw local fauna but also those from the Washakie County, Wyoming. Geological Survey of Wyoming, earliest Wasatchian (Wa0) of the Tuscahoma Formation in Memoir 2:1-151. Mississippi and Willwood Formation of the Bighorn Basin, Bown, T. M. and K. D. Rose. 1979. Mimoperadectes, a new marsu- Wyoming. pial, and Worlandia, a new dermopteran, from the lower part of the Willwood Formation (early Eocene), Bighorn Basin, ACKNOWLEDGMENTS Wyoming. Contributions from the Museum of Paleontology, The University of Michigan 25:89-104. The recovery of specimens from UCMP V71237 and Bown, T. M. and K. D. Rose. 1987. Patterns of dental evolution in V71238 was accomplished with support from the National early Eocene anatomorphine primates (Omomyidae) from the Science Foundation to the late D.E. Savage and from the An- Bighorn Basin, Wyoming. Journal of Paleontology 61 (Supple- nie M. Alexander Endowment of the UCMP. We thank J.H. ment to no. 5):1-162. (The Paleontological Society Memoir 23). Hutchison for his assistance in the field and his insights into Brandt, J.F. 1855. Beiträge zur nahern Kenntniss der Säugethiere the collecting history of these sites. M. Dawson, A. Tabrum, P. Russlands. Mémoires de l’Académie Impériale des Sciences de D. Gingerich and G. F. Gunnell, K. D. Rose, and L. Vietti are Saint-Pétersbourg 69:1-375. thanked for access to comparative material. Figure 4a laser Chew, A. 2005. Biostratigraphy, paleoecology and synchronized scan was made by N. Smith, Figure 4b was prepared by M. evolution in the early Eocene mammalian fauna of the cen- tral Bighorn Basin, Wyoming. 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